Determining an enthalpy change of reaction

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Introduction

Experiment 6 Title : Determining an enthalpy change of reaction Objective : The purpose of this experiment is to determine the enthalpy change for the displacement reaction between zinc and copper(II) sulphate. Theory : By adding an excess of zinc powder to a measured amount of aqueous copper(II) sulphate, and measuring the temperature change over a period of time, you can then calculate. The enthalpy change for the reaction. Reaction involved : Zu(s) + Cu2+(aq) --> Zn2+(aq) + Cu(s) The enthalpy change (H , kJmol-1) accompanying a process is the heat released or absorbed under constant pressure. The enthalpy change of an endothermic reaction must be larger than zero. ...read more.

Middle

4. The polystyrene cup was covered by a lid and a thermometer was put through the hole in the lid. The polystyrene cup was put in the beaker. 5. The solution was kept stirring and the temperature was recorded to the nearest 0.1 oC every half minute for 2 1/2 minutes. 6. At accurately 3 minutes, the zinc powder was added to the cup. 7. The mixture was kept on stirring and the temperature was recorded for an additional 6 minutes to complete a copy of Result Table. Calculation : Result Table Time/min 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Temperature/ oC 26.0 26.0 26.0 26.0 26.0 26.0 - 38.6 46.7 Time/min 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 Temperature/ oC 54.1 66.5 ...read more.

Conclusion

H = -E / N = -5643 / 0.025 = -22.6 kJ mol-1 Discussion : In this experiment, we should use the zinc powder instead of zinc granule. Since the zinc powder has a larger surface area, and it can increase the rate of reaction. We can use some good insulator to reduce heat loss to the surroundings, such as polystyrene cup. We can also cover the cup by a lid to reduce the heat loss to the surroundings by convection. Our hand should not touch the cup directly, it is used to prevent heat loss to our hands by conduction. Conclusion : The enthalpy change of the reaction is - 22.6kJ mol-1. ?? ?? ?? ?? ...read more.

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Exposure Inhalation: Dusts or mists (solutions) are probably non-irritating or mildly irritating. No human information is available, but inhaled zinc sulphate caused no observable toxic effects in animal tests. Reversible loss of the sense of smell may occur, based on data from animal tests.(2) Skin Contact: Zinc sulphate is not likely to cause irritation to the skin.